Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Earlier investigations involving chronic muscle stimulation have shown that skeletal muscle cells possess a much greater metabolic plasticity than had previously been recognized. We have described more fully the time course for the changes in different enzyme systems in single fibres of rabbit fast-twitch tibialis anterior (TA) muscles after periods of continuous stimulation of up to 10 weeks. After 2-5 wk every fibre shows higher levels of many oxidative enzymes than any control fibre; in some cases these levels are 2-10 times higher (well above any found even in the control soleus, a slow-twitch muscle). Citrate synthase, hexokinase and 3-oxoacid CoA-transferase are representatives of this group of enzymes. Other enzymes, such as malate dehydrogenase and amino acid aminotransferases also increase dramatically, but peak single fibre levels do not reach much above the highest in controls. These differential effects confirm at the single fibre level that chronic stimulation can alter mitochondrial composition. According to their staining reaction for myofibrillar ATPase, TA fibres are approximately 25% type IIA, and 75% type IIB, but by 5 wk these are converted to a mixture of type I, IIA and IIC fibres. At 5 wk, levels of glycolytic and high-energy phosphate transfer enzymes had decreased by 80% or more, and seemed to be adjusted to levels appropriate to their (new) ATPase type. This is in contrast to many enzymes of oxidative metabolism, which increase without synchronization with fibre type change. Determinations of metabolite concentrations in individual fibres from muscles freeze-clamped after varying periods of stimulation gave results which differ strikingly from data for acute stimulation. The findings reinforce our previous view that the high levels of ATP utilization engendered by chronic stimulation of muscle elicit a matching response in ATP production through a series of profound adaptations. Some of these are never encountered under the less extreme conditions of endurance exercise. Such features add to the interest and value of the chronic stimulation model as a means of studying the metabolic plasticity of muscle.
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PMID:Chronic stimulation of mammalian muscle: enzyme and metabolic changes in individual fibres. 252 28

The interaction of cyclopiazonic acid with rat skeletal muscle sarcoplasmic reticulum (SR) vesicles was investigated in order to study the mechanism of cyclopiazonic acid inhibition of the Ca2+-ATPase (Goeger et al., Biochem Pharmacol 37: 978-981, 1988). Cyclopiazonic acid at 25 microM prevented the binding of Ca2+ to the high affinity binding site of mixed (light and heavy) SR vesicles and inhibited, in a dose-dependent manner, the Ca2+-dependent phosphorylation of SR vesicles by ATP. Binding of Ca2+ to the high affinity site of the CA2+-ATPase is necessary for both Ca2+ transport and for phosphorylation of the Ca2+-ATPase. We conclude that inhibition of Ca2+ binding to the high affinity site may be responsible, at least in part, for the activity of cyclopiazonic acid. The mechanism of inhibition remains unclear. The inhibition was not reduced after dialysis and was only partially reversed by gel filtration of SR vesicles treated with cyclopiazonic acid. Neither 1 mM glutathione nor dithiothreitol pretreatment had any effect on the inhibition of the Ca2+-ATPase. In addition to its inhibition of Ca2+ uptake and the Ca2+-ATPase, cyclopiazonic acid had significant effects on Ca2+ efflux from both passively and actively loaded SR vesicles. Cyclopiazonic acid impeded the efflux of Ca2+ from passively loaded SR vesicles (in the presence of ruthenium red) when compared to either untreated vesicles or those treated with mersalyl acid, a mercurial which also inhibits the Ca2+-ATPase and is known to induce Ca2+ release by both ruthenium red-sensitive and -insensitive pathways. Treatment of actively loaded vesicles with cyclopiazonic acid resulted in a decreased rate of Ca2+ efflux when compared to SR vesicles in which the Ca2+-ATPase activity was inhibited by ATP depletion with hexokinase and glucose. The results are consistent with the hypothesis that, in mixed SR vesicles, cyclopiazonic acid inhibits both the Ca2+ pump and Ca2+ efflux.
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PMID:Interaction of cyclopiazonic acid with rat skeletal muscle sarcoplasmic reticulum vesicles. Effect on Ca2+ binding and Ca2+ permeability. 253 15

We have examined the effect of second messengers on ATP-driven H+ transport in an H+ ATPase-bearing endosomal fraction isolated from rabbit renal cortex. cAMP (0.1 mM) had no effect on H+ transport. Acridine orange fluorescence in the presence of 0.5 mM Ca2+ (+1 mM EGTA) was 19 +/- 6% of control. Inhibition of ATP-driven H+ transport by Ca2+ was concentration dependent; 0.25 and 0.5 mM Ca2+ (+1 mM EGTA) inhibited acridine orange fluorescence by approximately 50 and approximately 80%, respectively. Ca2+ also produced a concentration-dependent increase in the rate of pH-gradient dissipation. Ca2+ did not affect ATP hydrolysis. ATP-dependent Br- uptake was virtually unchanged in the presence of 0.5 mM Ca2+ (+1 mM EGTA). These vesicles were also shown to transport Ca2+ in an ATP-dependent mode. Inositol 1,4,5-trisphosphate had no effect on ATP-dependent Ca2+ uptake. These results are consistent with the co-existence of an H+ ATPase and an H+/Ca2+ exchanger on these endosomes, the latter transport system using the H+ gradient to energize Ca2+ uptake. Attempts to demonstrate an H+/Ca2+ antiporter in the absence of ATP have been unsuccessful. Yet, when a pH gradient was established by preincubation with ATP and residual ATP was subsequently removed by hexokinase + glucose, stimulation of Ca2+ uptake could be demonstrated. A Ca2(+)-dependent increase in H+ permeability and an ATP-dependent Ca2+ uptake might have important implications for the regulation of vacuolar H+ ATPase activity as well as the homeostasis of cytosolic Ca2+ concentration.
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PMID:H+/Ca2+ exchange in rabbit renal cortical endosomes. 253 22

Acylphosphatase activity and content were measured in erythrocytes from hyperthyroid patients and healthy controls. In addition, the soluble enzymes glucose-6-phosphate dehydrogenase, hexokinase, and the membrane bound (Na+ + K+)-ATPase and Ca2+-ATPase were assayed. Our results confirmed previous studies indicating a decrease of (Na+ + K+)-ATPase and an increase of Ca2+-ATPase activity in hyperthyroid erythrocytes. While glucose-6-phosphate dehydrogenase was not significantly changed, hexokinase and acylphosphatase activities were significantly higher in the hyperthyroid group. Both activities and content of acylphosphatase returned to normal levels in erythrocytes from treated patients, when they were euthyroid. These findings suggest that an excess of thyroid hormones may stimulate acylphosphatase biosynthesis in erythroid cells and indicate a potential clinical usefulness of this enzyme in hyperthyroidism.
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PMID:Increased acylphosphatase levels in erythrocytes from hyperthyroid patients. 255 5

The purified ATPase (F1F0) of Propionigenium modestum has its pH optimum at pH 7.0 or at pH 6.0 in the presence or absence of 5 mM NaCl, respectively. The activation by 5 mM NaCl was 12-fold at pH 7.0, 3.5-fold at pH 6.0, and 1.5-fold at pH 5.0. In addition to its function as a primary Na+ pump, the ATPase was capable of pumping protons. This activity was demonstrated with reconstituted proteoliposomes by the ATP-dependent quenching of the fluorescence of 9-amino-6-chloro-2-methoxyacridine. No delta pH was formed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone or by blocking the ATPase with dicyclohexylcarbodiimide. In the presence of valinomycin and K+, the delta pH increased, in accord with the operation of an electrogenic proton pump. The proton pump was only operative at low Na+ concentrations (less than 1 mM), and its activity increased as the Na+ concentration decreased. Parallel to the decrease of H+ pumping, the velocity of the Na+ transport increased about 6-fold from 0.1 to 4 mM NaCl, indicating a switch from H+ to Na+ pumping, as the Na+ concentration increases. Due to proton leaks in the proteoliposomal membranes, fluorescence quenching was released after blocking the ATPase with dicyclohexylcarbodiimide, by trapping residual ATP with glucose and hexokinase, or by the Na+-induced conversion of the proton pump onto a Na+ pump. Amiloride, an inhibitor of various Na+-coupled transport systems, was without effect on the kinetics of Na+ transport by the P. modestum ATPase.
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PMID:The sodium ion translocating adenosinetriphosphatase of Propionigenium modestum pumps protons at low sodium ion concentrations. 255 65

When temperature differences are taken into account, turtle brains use glucose at one-sixth the rate reported in rat brains. Na+-K+-ATPase activities are 2- to 2.5-fold higher in rat than in turtle brains. Maximal activities of hexokinase and lactate dehydrogenase are similar, whereas citrate synthase activities are two- to threefold higher in rat than turtle brains at the respective biological temperatures. Voltage-dependent Ca2+ channel densities, when compared between the two species, showed no consistent pattern. These data, along with the threefold differences in density of voltage-dependent Na+ channels reported by Lutz et al., are consistent with the idea that lower rates of channel and pump-mediated Na+ and K+ fluxes result in lower rates of aerobic energy metabolism in turtle brains compared with rat brains.
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PMID:Turtles and rats: a biochemical comparison of anoxia-tolerant and anoxia-sensitive brains. 255 54

Mebendazole (3.3 mumol), causes in vitro glycogen depletion and inhibits glucose uptake in Avitellina lahorea. Inhibition of non-specific phosphomonoesterases and adenosine triphosphatase by mebendazole discussed in the light of the role of phosphatases in uptake mechanisms. Mebendazole has no effect on hexokinase which has broad substrate specificity but influences the activities of some glycolytic enzymes such as phosphorylase, phosphoglucomutase and glucose-6-phosphatase. Thus, it appears that mebendazole also acts to disrupt certain enzymes of carbohydrate metabolism which may ultimately cause death of the parasite.
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PMID:In vitro effects of mebendazole on the carbohydrate metabolism of Avitellina lahorea (Cestoda). 282 93

The post-mortem stability of some brain enzymes was studied. Over the time period under examination, the cytoplasmic enzymes investigated underwent a decisive decay, hexokinase being the most labile and acylphosphatase the most stable. On the other hand, structured activities such as Na+, K+-ATPase and Ca2+, Mg2+-ATPase showed an apparent transitory increase. The differences in post-mortem stability of soluble enzymes could be ascribed, at least in part, to their different susceptibility toward proteolytic activities, as suggested by the electrophoretic results.
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PMID:Post-mortem modifications of the specific activity of some brain enzymes. 283 61

Inhibition of glutamate transport is a potential indirect cause of excitotoxic damage by glutamate in the CNS. The mercuric ion, the form in which metallic mercury vapor is believed to exert its neurotoxic action, is a known inhibitor of amino acid transport. This study examines the specificity with which HgCl2 inhibits glutamate transport in mouse cerebral astrocytes by means of comparative measurements of 2-deoxyglucose uptake. Uptake of 2-deoxyglucose is an index of glucose utilization that reflects the function of Na+,K+-ATPase and hexokinase, and is sensitive to Na+ entry. The kinetic parameters, ionic dependence, and substrate specificity of glutamate transport in these astrocyte cultures were consistent with the commonly occurring system designated X-AG. Acute exposure to 0.5 microM HgCl2 inhibited by 50% the initial rate of glutamate transport but did not affect 2-deoxyglucose uptake. Glutamate transport was not detectably inhibited by Al2+, Pb2+, Co2+, Sr2+, Cd2+, or Zn2+ (10 microM as chlorides). The inhibitory action of 0.5 microM HgCl2 on glutamate transport was rapidly reversible. The action of 1-2 microM HgCl2 was progressive when exposures were extended to 1-3 h, and was more slowly reversible. These results suggest that Hg2+ can impair glial glutamate transport reversibly at exposure levels that do not compromise some other vital cell functions.
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PMID:Specificity and reversibility of the inhibition by HgCl2 of glutamate transport in astrocyte cultures. 289 9

Seven hyperthyroid patients were studied by repeated muscle biopsies (vastus lateralis) before and after a period of medical treatment which averaged 10 months. The biopsies were analysed with regard to fibre-type composition, fibre area, capillary density, glycogen content and enzyme activities representing the glycolytic capacity (hexokinase, 6-phosphofructokinase), oxidative capacity (oxoglutarate dehydrogenase, citrate synthase) and Ca2+- and Mg2+-stimulated ATPase in muscle. In the pretreatment biopsy (hyperthyroid state), there was a significantly lower proportion of type I fibres (30% vs. 41%), a higher capillary density (23%), lower glycogen content (33%), and higher hexokinase activity (32%) compared with the post-treatment biopsy. No significant changes in the activity of the remaining enzymes were observed. The present study indicates that hyperthyroidism induces a transformation from type I to type II fibres in human skeletal muscle. The increase in hexokinase activity probably reflects a higher glucose utilization by skeletal muscle in order to compensate partially for the reduced glycogen content.
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PMID:Effect of hyperthyroidism on fibre-type composition, fibre area, glycogen content and enzyme activity in human skeletal muscle. 293 5


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